On September 15, 1997, EPA adopted new source performance standards (NSPS) and emissions guidelines (EG) for hospital/medical/ infectious waste incinerators (HMIWI). The NSPS and EG were established under Sections 111 and 129 of the Clean Air Act (CAA or Act). In a response to a suit filed by the Sierra Club and the Natural Resources Defense Council (Sierra Club), the U.S. Court of Appeals for the District of Columbia Circuit (the Court) remanded the HMIWI regulations on March 2, 1999, for further explanation of EPA's reasoning in determining the minimum regulatory "floors" for new and existing HMIWI. The HMIWI regulations were not vacated and were fully implemented by September 2002. On February 6, 2007, we published our proposed response to the Court's remand. Following recent court decisions and receipt of public comments regarding the proposal, we re- assessed our response to the remand, and on December 1, 2008, we published another proposed response and solicited public comments. This action promulgates our response to the Court's remand and also satisfies the CAA Section 129(a)(5) requirement to conduct a review of the standards every 5 years.